Cultured neurons showing distinct neurotransmitter phenotypes. Double immunolabelling of GABA (green, A) and glutamate (red, B) of neurons from a 10-week-old fetus cultured for 30 days. These images are merged in C. Neurons immunoreactive for GABA only remained red, for glutamate only remained green, and those immunoreactive for both became yellow. Scale bars, 20 μm.